Fuel supply system for engine

ABSTRACT

When a flywheel rotates and a first magnet comes close to and opposes a fuel pump, a plunger is moved toward a partition wall of a pump chamber against an urging force of a spring by a magnetic repulsive force generated between the first magnet and a second magnet in the fuel pump. When the first magnet separates from the fuel pump, the plunger is moved and returned toward a protective cover by the urging force of the spring. As a result, the plunger in the fuel pump reciprocates with rotation of the flywheel, and the capacity of the pump chamber increases and decreases, so that fuel is sucked and discharged.

CROSS-REFERENCES TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2009-024930 filed onFeb. 5, 2009 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel supply system for an engine,which pressurizes fuel from a fuel tank and supplies the fuel to a fuelinjection valve without using driving power from a battery.

2. Description of the Related Art

In most general-purpose engines of a spark ignition type for use inpower generators and operating machines, a battery is not mounted,starting is performed by manually pulling a recoil starter, and powerfor ignition is supplied by a magneto. In a case in which the amount offuel injected from a fuel injection valve provided in such ageneral-purpose engine is electronically controlled in accordance withthe operating condition of the engine, it is a problem how to ensurepower for the devices.

In this case, the fuel injection valve and an electronic control devicefor controlling the fuel injection valve can be driven by the voltageprovided immediately after starting is performed by pulling the recoilstarter. However, it is difficult to ensure sufficient power for a fuelpump for generating fuel pressure that is the point of fuel control. Forthis reason, there is no other choice but to use, as the fuel pump, amechanical fuel pump that is driven by the engine.

For example, in a battery-less electronic fuel injection control devicedisclosed in Japanese Unexamined Patent Application Publication No.5-164010, fuel is pressurized by a mechanical pump that is driven inconjunction with the rotation of a flywheel connected to a crankshaft ofthe engine, and the fuel is then supplied to a fuel injection valve.

Japanese Examined Utility Model Registration Application Publication No.7-52374 discloses a technique using a film-valve pulse pump forpressurizing and supplying fuel by the change in internal pressure of acrankcase, and a plunger-type fuel pump to be driven by a cam attachedto a crankshaft. Fuel in a fuel tank is pressure-fed to the plunger-typefuel pump by the film-valve pulse pump, is further pressurized by theplunger-type fuel pump, and is then supplied to a fuel injection valve.

However, in the mechanical fuel pump driven by the engine, the mechanismis complicated to obtain a stable pressure suitable for fuel injection,and this leads to a rise in cost. Moreover, the performance may bereduced by the influences of trouble and heat.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-describedcircumstances, and an object of the invention is to provide an enginefuel supply system capable of obtaining a stable pressure suitable forfuel injection.

In order to achieve the above object, an engine fuel supply systemaccording to the present invention pressurizes fuel from a fuel tank andsupplies the pressurized fuel to a fuel injection valve without usingdriving power from a battery. The engine fuel supply system includes afirst magnetic member fixed to an outer peripheral portion of a rotorconnected to a rotation shaft of an engine; and a fuel pump opposing theouter peripheral portion of the rotor and including a second magneticmember that magnetically acts on the first magnetic member. At least oneof the first magnetic member and the second magnetic member is formed bya permanent magnet. The fuel pump reciprocates the second magneticmember by a magnetic force between the first magnetic member and thesecond magnetic member, the magnetic force changing with rotation of therotor, and sucks the fuel from the fuel tank and discharges the fuelwith a predetermined pressure by the reciprocation.

According to the present invention, it is possible to obtain a stablepressure suitable for fuel injection without using a complicatedmechanism, and to thereby realize an inexpensive fuel supply system withhigh reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural view of an engine fuel supply system; and

FIG. 2 is an enlarged view showing an exemplary structure of a fuelpump.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below withreference to the drawings.

An engine 1 shown in FIG. 1 is a general-purpose engine of a sparkignition type, and is used as, for example, a motor for a powergenerator, an operating machine, or a snowmobile. In FIG. 1, the engine1 is an air-cooled V-engine, in which a suction port 4 and an exhaustport 5 are open in a cylinder head 3 a provided in an upper part of acylinder 3 inclined with respect to a crankcase 2. The suction port 4communicates with an air cleaner (not shown), and the exhaust port 5communicates with a muffler 6 provided above the cylinder head 3 a.

A crankshaft 1 a protrudes from the crankcase 2 of the engine 1. Thecrankshaft 1 a is connected, via a connecting rod, to a piston thatslidably reciprocates in the cylinder 3, and is rotatably supported bythe crankcase 2. A cooling fan 7 is fitted on and rotatably supported bya protruding shaft of the crankshaft 1 a. On the circumference of thecooling fan 7, a plurality of fins 7 a are arranged at regularintervals. A flywheel 9 (see FIG. 2) is provided integrally with a backside of the cooling fan 7. A magnet (permanent magnet) 8 for ignition isfixed to an outer peripheral portion of the flywheel 9.

A control unit 10 and a fuel pump 20 are provided beside the cooling fan7 of the crankcase 2 in a manner such as to face the magnet 8 of theflywheel 9 with a predetermined gap being therebetween. The control unit10 includes a magneto coil and an ignition coil facing the magnet 8 ofthe flywheel 9 with a predetermined gap being therebetween, an ignitioncircuit, such as a transistor or a mechanical contact, for energizes andinterrupts one side of the ignition coil, a power supply circuit forgenerating control power by rectifying and smoothing magneto power, andan electronic control circuit for engine control that mainly includes amicrocomputer.

An ignition plug 11 is connected to an output side of the ignitioncircuit incorporated in the control unit 10. The ignition plug 11 isprovided in the cylinder head 3 a, and has, at its leading end, adischarging electrode exposed in a fuel chamber. Further, an injector(fuel injection valve) 12 is connected to an output side of theelectronic control circuit incorporated in the control unit 10. Theinjector 12 injects fuel, which is press-fed from the fuel pump 20, intoa suction passage of the engine 1.

In FIG. 1, for convenience of understanding of the fuel supply system,the injector 12 that is actually provided near the suction port 4 of theengine 1 is shown separately from the engine 1.

Next, a description will be given of the fuel pump 20 that is a majorcomponent of the fuel supply system. The fuel pump 20 includes asuction-side joint portion 21 a serving as a fuel suction port, adischarge-side joint portion 21 b serving as a fuel discharge port, andflange portions 21 c serving portions mounted to the crankcase 2. Thesuction-side joint portion 21 a is connected to a fuel tank 14 via apipe 13, and the discharge-side joint portion 21 b is connected to theinjector 12 via a pipe 15.

A fuel filter 16 is interposed in the pipe 13 that connects the fueltank 14 and the fuel pump 20, and a pulsation damper 17 for dampingpulsation of fuel pressure is interposed in the pipe 15 that connectsthe fuel pump 20 and the injector 12. For example, the fuel tank 14 isprovided above the engine 1.

As will be described below, a first magnetic member is fixed to an outerperipheral portion of a rotor that is connected to the crankshaft 1 aserving as the rotation shaft of the engine 1, and the fuel pump 20includes a second magnetic member that can magnetically act on the firstmagnetic member. At least one of the first magnetic member and thesecond magnetic member is formed by a permanent magnet. The fuel pump 20is a reciprocating pump that is operated by magnetic force of thepermanent magnet in a non-contact manner.

In the embodiment, as illustrated in FIG. 2, the first magnetic memberis the ignition magnet (permanent magnet) 8 fixed to the outerperipheral portion of the flywheel 9 serving as the rotor connected tothe crankshaft 1 a, and the second magnetic member is a magnet(permanent magnet) 31 fixed to a plunger 30 in the fuel pump 20. Thefuel pump 20 is a plunger-type pump in which the plunger 30 reciprocatesby magnetic forces of the magnets 8 and 31 with rotation of the flywheel9.

More specifically, the fuel pump 20 includes a pump housing 21 and aprotective cover 22. The suction-side joint portion 21 a, thedischarge-side joint portion 21 b, and the flange portions 21 c formounting are provided outside the pump housing 21, and the plunger 30 isprovided in the pump housing 21 in a manner such as to move forward andbackward. The protective cover 22 covers an opening provided in a sideof the pump housing 21 opposite the suction-side joint portion 21 a andthe discharge-side joint portion 21 b. The pump housing 21 is formed ofa nonmagnetic material such as aluminum, and the protective cover 22 isformed of a magnetically permeable material such that the magnetic forcefrom the magnet 8 of the flywheel 9 acts on the interior of the fuelpump 20.

The pump housing 21 includes a pump chamber 23 accommodating the plunger30, a suction-valve chamber 25 accommodating a check valve 24 thattransmits fuel from the suction-side joint portion 21 a only toward thepump chamber 23, and a discharge valve chamber 27 accommodating a checkvalve 26 that transmits fuel from the pump chamber 23 only toward thedischarge-side joint portion 21 b.

The plunger 30 is shaped like a hollow cylinder having one closed end,and the magnet (permanent magnet) 31 is fixed to the closed end. Theplunger 30 is provided in the pump chamber 23 with the magnet 31 facingthe protective cover 22 in a manner such as to move into and out of thepump chamber 23. A spring 28 for urging the plunger 30 toward theprotective cover 22 is provided between a back surface of the closed endin the plunger 30 and a partition wall 23 a for the valve chambers 25and 27 of the pump chamber 23. Further, a seal member 29, such as anO-ring or an oil seal, is provided on an inner peripheral surface of thecylinder of the pump chamber 23. The seal member 29 serves to maintainoil tightness between the inner peripheral surface of the pump chamber23 and an outer peripheral surface of the cylinder of the plunger 30.

The magnet 31 fixed to the plunger 30 and the magnet 8 fixed to theouter peripheral portion of the flywheel 9 are set in a manner such thatthe same poles thereof oppose each other.

The fuel pump 20 having the above-described configuration is locatedsuch that the moving axis direction of the plunger 30 points toward therotation center of the flywheel 9 and such that a specified distance isprovided between the fuel pump 20 and the magnet 8 of the flywheel 9.The fuel pump 20 is fixed to the crankcase 2 by bolts with the flangeportions 21 c being disposed therebetween. Next, a description will begiven of how the engine 1 is driven by the fuel supply from theabove-described fuel pump 20.

First, when the flywheel 9 is rotated by pulling the recoil starter (notshown), the magnet 8 fixed to the outer peripheral portion of theflywheel 9 circles to pass across the fronts of the control unit 10 andthe fuel pump 20. Then, control power is generated from magnet powerthat is produced by the rotation of the flywheel 9, and operates theignition circuit and the electronic control circuit in the control unit10.

In this case, at a position where the magnet 8 of the flywheel 9 islocated close to and opposes the fuel pump 20, the plunger 30 having themagnet 31 fixed thereto moves toward the partition wall 23 a of the pumpchamber 23 against the urging force of the spring 28 because of magneticrepulsive force generated between the magnet 8 of the flywheel 9 and themagnet 31 in the fuel pump 20. In contrast, when the magnet 8 separatesfrom the fuel pump 20, the repulsive force between the magnets 8 and 31reduces or disappears, so that the plunger 30 moves and returns towardthe protective cover 22 because of the urging force of the spring 28.

As a result, with the rotation of the flywheel 9, the plunger 30 in thefuel pump 20 reciprocates toward the partition wall 23 a and theprotective cover 22, whereby the capacity of the pump chamber 23increases and decreases to suck and discharge the fuel. In other words,when the plunger 30 moves toward the protective cover 22, the capacityof the pump chamber 23 increases, the pressure in the pump chamber 23decreases, the check valve 24 of the suction valve chamber 25 opens, sothat fuel is sucked from the fuel tank 14 into the pump chamber 23through the suction-side joint portion 21 a. The fuel in the pumpchamber 23 is pressurized by the movement of the plunger 30 toward thepartition wall 23 a, and the check valve 26 of the discharge valvechamber 27 opens at a predetermined pressure, so that the fuel isdischarged from the discharge-side joint portion 21 b and is supplied tothe injector 12.

Then, the injector 12 is driven to inject the fuel at a valve openingtime calculated by a CPU of the electronic control circuit in thecontrol unit 10. Further, the ignition plug 11 sparks in response to asignal from the ignition circuit, and a mixture of the fuel injectedfrom the injector 12 and the sucked air is ignited and burnt, wherebythe engine 1 is driven.

In this way, in the embodiment, the fuel supply system for supplying thefuel to the injector 12 is configured by utilizing the magnet 8 fixed tothe outer peripheral portion of the flywheel 9 of the magneto ignitionengine. That is, it is possible to realize an inexpensive fuel supplysystem in which the plunger 30 of the fuel pump 20 reciprocates by amagnetic force of the ignition magnet 8 with the rotation of theflywheel 9.

In the fuel pump 20 of this fuel supply system, there is no need toobtain pump driving force by mechanical connection to the rotation shaftof the engine, a stable driving force can be obtained without contactwith the rotating section of the engine, and a stable pressure suitablefor fuel injection can be obtained. In addition, since the pump isdriven without contact with the rotating section of the engine, it ispossible to suppress performance degradation due to trouble and heat,and to realize an inexpensive fuel supply system with high reliability.

The fuel pump 20 that constitutes of the fuel supply system in theabove-described embodiment is just exemplary, and various othermodifications are possible. For example, the fuel supply system can havethe following configurations (1) to (3):

(1) The magnet 31 fixed to the leading end of the plunger 30 in the fuelpump 20 and the magnet 8 fixed to the outer peripheral portion of theflywheel 9 are set in a manner such that opposite poles thereof faceeach other, and the spring 28 for urging the plunger 30 is formed by atension spring.

(2) The magnet 31 fixed to the leading end of the plunger 30 in the fuelpump 20 is eliminated, and a magnetic member, such as a steel member, isfixed to the leading end of the plunger 30. Alternatively, the plunger30 itself is formed by a magnetic material. Also, the spring 28 forurging the plunger 30 is formed by a tension spring.

(3) The fuel pump 20 is formed by a reciprocating pump using adiaphragm, instead of the plunger 30.

1. An engine fuel supply system that pressurizes fuel from a fuel tankand supplies the pressurized fuel to a fuel injection valve, the enginefuel supply system comprising: a first magnetic member fixed to an outerperipheral portion of a rotor connected to a rotation shaft of anengine; and a fuel pump opposing the outer peripheral portion of therotor and including a second magnetic member that magnetically acts onthe first magnetic member, wherein at least one of the first magneticmember and the second magnetic member is formed by a permanent magnet,and wherein the fuel pump reciprocates the second magnetic member by amagnetic force between the first magnetic member and the second magneticmember, the magnetic force changing with rotation of the rotor, andsucks the fuel from the fuel tank and discharges the fuel with apredetermined pressure by the reciprocation.
 2. The engine fuel supplysystem according to claim 1, wherein the first magnetic member is apermanent magnet for generating ignition power.
 3. The engine fuelsupply system according to claim 1, wherein the fuel pump is aplunger-type pump that sucks and discharges the fuel by reciprocating aplunger including the second magnetic member.